title: Mechanisms of resistance to 5-aza-2'-deoxycytidine in human cancer cell lines.
abstract: 5-aza-2'-deoxycytidine (DAC) is approved for the treatment of myelodysplastic syndromes, but resistance to this agent is common. In search for mechanisms of resistance, we measured the half maximal (50%) inhibitory concentration (IC(50)) of DAC and found it differed 1000-fold among a panel of cancer cell lines. The IC(50) was correlated with the doses of DAC that induced the most hypomethylation of long interspersed nuclear elements (LINE; R = 0.94, P < .001), but not with LINE methylation or DNA methyltransferase 1 (DNMT1), 3a, and 3b expression at baseline. Sensitivity to DAC showed a low correlation (R = 0.44, P = .11) to that of 5-azacytidine (AZA), but a good correlation to that of cytarabine (Ara-C; R = 0.89, P < .001). The 5 cell lines most resistant to DAC had a combination of low dCK, hENT1, and 2 transporters, and high cytosine deaminase. In an HL60 clone, resistance to DAC could be rapidly induced by drug exposure and was related to a switch from heterozygous to homozygous mutation of DCK. Transfection of wild-type DCK restored DAC sensitivity. DAC induced DNA breaks as evidenced by H2AX phosphorylation and increased homologous recombination rates by 7- to 10-fold. These results suggest that in vitro resistance to DAC can be explained by insufficient incorporation into DNA.
authors.affiliation: Department of Leukemia, University of Texas M. D. Anderson Cancer Center, Houston, USA.
authors.forename: Taichun
authors.initials: T
authors.lastname: Qin
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Jelinek
authors.forename: Jiali
authors.initials: J
authors.lastname: Si
authors.forename: Jingmin
authors.initials: J
authors.lastname: Shu
authors.forename: Jean-Pierre J
authors.initials: JP
authors.lastname: Issa
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage*; D001374:Azacitidine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D004247:DNA / Q000187:drug effects*; D004249:DNA Damage; D019175:DNA Methylation; D000077209:Decitabine; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D006801:Humans; D020128:Inhibitory Concentration 50; D019656:Loss of Heterozygosity; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D000964:Antimetabolites, Antineoplastic; D000077209:Decitabine; D004247:DNA; D001374:Azacitidine